Right now
The most recent data we hold from NOAA arrived 6 minutes ago, and this point is not in it. We record detections, not passes: an absence is not proof that nothing is there.
Nothing else has been detected within 20 km in the last 24 hours.
This alert expired on 18 May 2026 at 03:45 UTC. It is kept here as a record.
It is the strongest of the 16 detections recorded within 20 km of this point since 15 March 2026. Another comparable one was recorded here earlier the same day. One more was recorded here in the fortnight before it.
What the source measured
NOAA reported: Tornado Warning issued May 17 at 10:27PM CDT until May 17 at 10:45PM CDT by NWS Des Moines IA
An estimated 69,603 people live within 50 km of this point.
Nearby, since 15 March 2026
- July 20, 2026 · score 39 · 6.1 km
- July 9, 2026 · score 34 · 23.4 km
How we know
Confirmed by 2 independent sources, including NOAA.
Our own score for this event is 63 out of 100, at 86 % confidence.
The score is ours, computed from intensity, exposed population and local history — not the source’s.
Computed under scoring rules v1. Rows carrying other versions were judged by different rules and are not directly comparable.
Event Data
| Type | Severe Weather |
| Severity | Critical |
| Calamity Score (ours) | 63 / 100 |
| Our confidence | 86% |
| Coordinates | 43.3281, -93.1069 |
| Nearest City | Mason City (21 km) |
| Population Exposed | 69.6K within 50 km |
| Impact Tier | severe |
| Timestamp | 2026-05-18T03:27:00.000Z |
| Source | https://api.weather.gov/alerts/merged_Tornado Warning_noaa_urn:oid:2.49.0.1.840.0.963ea33e5bf0da94292e8d459efc3fed |
Score Breakdown
Technical Details
| Event | Tornado Warning |
| Urgency | Immediate |
| Certainty | Observed |
| AreaDesc | Cerro Gordo, IA; Cerro Gordo, IA; Winnebago, IA; Worth, IA; Floyd, IA; Mitchell, IA and 2 more areas |
| Headline | Tornado Warning issued May 17 at 10:27PM CDT until May 17 at 10:45PM CDT by NWS Des Moines IA |
| Expires | 2026-05-17T22:45:00-05:00 |
| SenderName | NWS Des Moines IA |
| HasExactCoords | true |
| MergedCount | 5 |
| MergedIds | ["noaa_urn:oid:2.49.0.1.840.0.963ea33e5bf0da94292e8d459efc3feda0707f1d.001.1","noaa_urn:oid:2.49.0.1.840.0.fb01515b4669917b33b17994cf5c7b37f9bc9b90.002.1","noaa_urn:oid:2.49.0.1.840.0.d396676072cc303aa684e6cfde7841395e792466.001.1","noaa_urn:oid:2.49.0.1.840.0.74e62b5f2df2a833a291311f74a96c235c3fecbb.001.1","noaa_urn:oid:2.49.0.1.840.0.f753b08be1c87db023429149ffdccfc08dbfd3ca.001.1"] |
| Iem TypeSummary | T |
| Iem City | 4 N Crystal Lake |
| Iem County | Winnebago |
| Iem State | IA |
| Iem Wfo | DMX |
| Iem Remark | Reports of power line sparking/flashing. |
| MergedSources | [{"id":"iem_T_43.280_-93.790_1779073140000","source":"iem","severity":"low","severityValue":25,"timestamp":1779073140000,"latitude":43.28,"longitude":-93.79}] |
Safety Information
If a tornado warning is issued: go to a basement or an interior room on the lowest floor, away from windows. A vehicle and a mobile home are not shelter. Cover your head and neck. Wait for the official all-clear before going outside, and watch for downed power lines and gas leaks afterwards.
Series begins 8 March 2026. Comparisons refer to that period only. Collection gap: 14-26 August 2026.
This data is aggregated algorithmically from scientific sources. Not a replacement for official emergency warnings.
Want to know when something happens near Mason City?
Calamity.live data shows a weather event with CalamityScore 63/100, near Mason City (United States), based on data from noaa. Source: Calamity.live, a platform aggregating real-time data from 185 scientific monitoring sources.